The studies will provide information regarding the ultrastructure and drug metabolizing capacity of liver obtained from the fetal stumptailed macaque, Macaca arctoides, at various gestational ages. Comparisons will be made with human fetal liver whenever possible. The overall aim of the project is to evaluate the extent to which the development of metabolism of drugs of abuse in the liver of the fetal monkey is comparable to that of the human and to relate these findings, in as much as possible, to clinical medicine. The long term research objective is to develop the fetal nonhuman primate system into an animal model for the study of maternal-fetal drug interactions and their significance to the developing human fetus. BIBLIOGRAPHIC REFERENCES: Dvorchik, B.H. and Stenger, V.G.: Fetal hepatic metabolism of drugs of abuse. Third National Drug Abuse Conference. In press 1977. Dvorchik, B.H.: Regionalization of some of the components of the mixed-function oxidase system in fetal liver: Correlation with fetal hepatic circulation and oxygenation. "Circulation in the Fetus and Newborn". Raven Press. In Press 1977.